Auto-guard cut out

From Tardis Wiki, the free Doctor Who reference
The auto-guard cut out aboard Nerva Beacon. (TV: The Ark in Space)

An auto-guard cut out allowed for the deactivation of auto-guards.

While trapped, sheltering from the attacks of such a security drone aboard Nerva Beacon, the Fourth Doctor used Harry Sullivan's shoe to distract it so he could react the cut out and turn the auto-guard off. (TV: The Ark in Space)